FATIGUE PROPERTIES OF CARBON-COATED AND POROUS-COATED TI-6AL-4V ALLOY

The study investigated the effects that both a porous Ti-6Al-4V alloy coating and a ULTI carbon coating have on the fatigue properties of a Ti-6Al-4V alloy substrate system. The fatigue properties of uncoated as-received, uncoated sinter heat treated and notched Ti-6Al-4V material were also investigated. The results of this study revealed endurance limits for Ti-6Al-4V alloy tested with a rotating beam system of 617 MN/m**2 (uncoated as-received), 624 MN/m**2 (ULTI carbon-coated), 377 MN/m**2 (sinter heat treated), 220 MN/m**2 (notched) and 138 MN/m**2 (porous-coated). No effects on fatigue properties were observed when testing the material in saline compared with air. The slight increase in fatigue strength for the carbon-coated material is thought to be due to the increase in surface hardness resulting from the formation of titanium carbides on the surface. The low-endurance limit of the porous-coated material is due to both the transition from the as-received equiaxed microstructure to a lamellar microstructure upon sintering and to the notch effect created by the porous coating.